1. Field of the Invention
The present invention relates to an optical element and a wavelength monitor.
2. Related Background Art
Technologies are disclosed in which a first photodiode that monitors light transmitting an optical filter having a wavelength periodicity and a second photodiode that monitors total optical power incident on the optical filter are provided and by using outputs of these two photodiodes, a wavelength is monitored (for instance, refer to Patent Literature 1).
Also, technologies are disclosed in which a wavelength is monitored by using outputs of two photodiodes that monitor two light beam outputs transmitting optical filter means that materializes from a single etalon filter two light transmission characteristics in which amplitude periods are relatively shifted by π/2 (for instance, refer to Patent Literature 2).    Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2001-308444    Patent Literature 2: Japanese Patent Application Laid-Open Publication No. 2002-202190